1. Field
Exemplary embodiments of the present invention relate to a nonvolatile memory device and a method for fabricating the same, and more particularly, to a nonvolatile memory device including a plurality of memory cells stacked substantially perpendicularly from a substrate, and a method for fabricating the same.
2. Description of the Related Art
A nonvolatile memory device maintains data stored therein even though power supply is cut off. Currently, various nonvolatile memory devices such as a NAND flash memory and the like are widely used.
Recently, as the improvement in integration degree of a 2D nonvolatile memory device including memory cells formed as a signal layer over a silicon substrate approaches the limit, a 3D nonvolatile memory device including a plurality of memory cells stacked perpendicularly from a silicon substrate has been proposed.
FIGS. 1A to 1C are diagrams illustrating a conventional 3D nonvolatile memory device. FIG. 1A is a plan view, FIG. 1B is a cross-sectional view taken along line Y4-Y4′ of FIG. 1A. FIG. 1C is a cross-sectional view taken along lines Y5-Y5′ and Y6-Y6′ of FIG. 1A.
Referring to FIGS. 1A to 1C, a method for fabricating the conventional nonvolatile memory device will be briefly described as follows.
First, a structure in which a plurality of interlayer dielectric layers 120 and sacrifice layers 130 are alternately stacked (hereinafter, referred to as a stacked structure) is formed over a substrate 100 defining a cell area B and a peripheral area A at both sides of the cell area B and having a source region 110 provided therein.
The stacked structure of the peripheral area A is etched in a stair shape.
The stacked structure of the cell area B is selectively etched to form a plurality of channel holes CH exposing the substrate 100 through the stacked structure, and a memory layer 140 and a channel layer 150 are then formed in the channel holes CH.
The stacked structure of the cell area B is selectively etched to form a first slit SA. Furthermore, the stacked structure of the cell area B and the peripheral area A is selectively etched to form a second slit SB. At this time, the second slit SB is extended to the peripheral area A as well as the cell area B, because the sacrifice layers 130 of the peripheral area A are partially removed to form conductive layers 180 to be connected to a word line contact WC. Furthermore, since the second slit SB must provide an area where a source contact SC is subsequently formed, the second slit SB has a relatively large width. Accordingly, the sidewall of the second slit SB has an inclined profile.
The sacrifice layers 130 exposed through the first and second slits SA and SB are removed, and conductive layer 180 are buried in spaces where the sacrifice layers 130 were removed.
The first slit SA is filled with an insulating material (not illustrated). Furthermore, an insulating layer 11 is formed on the sidewall of the second slit SB, and the rest of the first slit SA is filled with a conductive material to form a source contact SC.
Then, a word line contact WC connected to the conductive layers 180 in the peripheral area A is formed, thereby completing the device of FIGS. 1A to 1C.
In the above-described device, since the second slit SB must provide an area where the source contact SC is subsequently formed, the second slit SB needs to have sufficiently large width. In general, when an area having a relatively large width is etched, the slope of the etched portion of the area increases more than when an area having a relatively small width is etched. Therefore, the second slit SB has an inclined profile of which the width decreases from the top toward to the bottom. Because of the inclined profile of the second slit SB, the respective conductive layers 180 of the peripheral area A are positioned to deviate from each other in a perpendicular direction. That is, the conductive layers 180 are gradually moved to the outside, based on the second slit SB, from the bottom to the top. Therefore, when the position of the word line contact WC is decided based on the uppermost conductive layer 180 during the formation of the word line contacts WC, the positions of the lowermost conductive layer 180 and the word line contact WC may deviate from each other such that the lowermost conductive layer 180 and the word line contact WC are not connected to each other (refer to D).
However, if the width of the second slit B is reduced, it becomes difficult to form the source contact SC.